LITHOFACIES EVOLUTION AND MINERALOGICAL–GRANULOMETRIC HETEROGENEITY OF JURASSIC RESERVOIR ROCKS IN THE SOUTHERN ZHETYBAY FIELD

Abstract

This study investigates the vertical variability of productive horizons within the Jurassic deposits of the Southern Zhetybay Field and establishes the main controls on the development of their reservoir properties. Based on an integrated sedimentological, petrographic, mineralogical, and scanning electron microscopy (SEM) study of core samples, relationships were identified between lithofacies characteristics, the degree of petrographic maturity, secondary diagenetic and catagenetic alterations, and the characteristics of the pore space.

A total of 24 facies were identified within the Jurassic succession and grouped into several facies associations reflecting changes in depositional environments. The reservoir properties of the rocks were found to be controlled not only by their primary depositional characteristics but also by subsequent lithogenetic alterations, including compaction, changes in grain-contact relationships, cementation, and redistribution of pore space. The detrital fraction is dominated by quartz, feldspars, rock fragments, and micas, with poor to moderate sorting and predominantly angular to subrounded grain shapes.

The scientific novelty of the study lies in establishing a systematic relationship between the facies architecture of the Jurassic deposits, the maturity of the grain framework, the nature of catagenetic alterations, and the development of reservoir properties. The identified relationships provide a basis for refining the depositional conditions and spatial heterogeneity of the productive horizons of the Southern Zhetybay Field and can be applied to reservoir-quality prediction and the improvement of geological and dynamic reservoir models.